1. Field of the Invention
The present invention relates to single-plate color CCD and CMOS solid-state imaging devices and, more specifically, to a solid-state imaging device of a photoconductive-layer-stacked type, including a stack of photoconductive layers serving as an optical-electrical conversion section on a substrate.
2. Description of the Related Art
In a single-plate color solid-state imaging device of a general type, color filters such as R (Red), G (Green), and B (Blue) are assigned to a pixel formed with a light receiving section. With the solid-state imaging device structured as such, the pixels each assigned with various color filters are put in groups to derive a color signal. This results in limited improvement of the spatial resolution. For betterment, recently proposed is a solid-state imaging device including a stack of photoconductive layers (optical-electrical conversion layers) serving as an optical-electrical conversion section with a one-to-one relationship between layers and colors. With such a solid-state imaging device, a color signal can be derived without grouping pixels but with a single pixel.
In the solid-state imaging device of such a photoconductive-layer-stacked type wherein the photoconductive layer to be the optical-electrical conversion section is formed on the substrate, FIG. 1 shows the structure of a light receiving section. Referring to FIG. 1, the light-receiving section is located on a semiconductor substrate 101, and structured by photoconductive layers 103R for red, 103G for green, and 103B for blue. On these photoconductive layers 103R, 103G, and 103B, a transparent electrode 105 is each provided. To be more specific, the photoconductive layer 103B is located at the top with a thickness enough to absorb light Hb in a wavelength region specifically for blue. The photoconductive layer 103G is located at the middle with a thickness enough to absorb light Hg in a wavelength region specifically for green. Located at the bottom is the photoconductive layer 103R with a thickness enough to absorb light Hr in a wavelength region specifically for red.
Through voltage application to the semiconductor substrate 101, and the transparent electrode layers 105 placed above and below of these photoconductive layers 103R, 103G, and 103B, any electric charge absorbed through these photoconductive layers 103R, 103G, and 103B is successively read after optical-electrical conversion. In such a manner, a color signal can be derived by a single pixel (for details, refer to Non-Patent Document 1 below).    [Non-Patent Document 1]    Dietmar Knipp, et al. “Stacked Amorphous Silicon Color Sensor”, IEEE TRANSACTION ON ELECTRON DEVICES, VOL. 49, NO. 1, JANUARY 2002, P. 170 to 176.